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Astronomers now confirm that the Sun’s magnetic dynamo is likely to eventually disappear causing our star to lose its 11 year magnetic cycle. In fact, a billion years from now, they say, interplanetary spaceflight could become even more treacherous, since the Sun’s protective magnetic heliosphere would weaken or even disappear --- leaving our solar system unshielded from incoming cosmic rays.

In a paper submitted to the journal Solar Physics, co-author Travis Metcalfe confirms that the Sun, a yellow dwarf (G-spectral type) star is indeed making a long term transition in its magnetic activity cycle.

Over the next one to two billion years, we have confirmed that the Sun’s magnetic cycle period will get longer before disappearing entirely, Metcalfe, a research scientist at the Space Science Institute in Boulder, Colo., told me. Such changes in the Sun’s evolutionary state, he says, could even altogether eliminate Earth’s signature auroras --- the source of our polar Northern and Southern lights.

A major solar eruption is shown in progress October 28, 2003. (Photo by Solar & Heliospheric Observatory/NASA via Getty Images)

Last year, in a paper appearing in The Astrophysical Journal, Metcalfe and colleagues first reported that for the last 400 million years, the Sun has been magnetically transitioning into a new evolutionary phase. That is, a phase thought to affect all middle-aged stars.

This new work, says Metcalfe, suggests that the Sun’s 11-year magnetic cycle may be growing longer on stellar evolutionary timescales, and that its cycle might disappear altogether sometime in the next 800 million to 2.4 billion years.

“Our previous discoveries identified an unexpected transition in the rotation and magnetism of middle-aged stars,” said Metcalfe. “We now have direct evidence that the stellar dynamo --- the mechanism inside stars that sustains their magnetic fields --- actually shuts down during this transition.”

Metcalfe says that to understand our own Sun’s life story, astronomers need numerous observations of sun-like stars of very different ages, masses, rotation rates and magnetic fields.

Three stars currently make the best references for what’s happening to our 4.6 billion year-old Sun. They include the slightly younger 4.1 billion year-old 18 Scorpii; the 5.4 billion year-old alpha Centauri A and the 7 billion year-old stars 16 Cygnus A & B.

They provide the strongest evidence yet that the Sun is currently going through a magnetic transition, says Metcalfe. The rotation rate for nearby star alpha Centauri A has stayed almost constant but its magnetic cycle takes 19 years. And in the stars 16 Cygnus A & B, Metcalfe sees no magnetic cycle at all.

“During the first half of their lives, the rotation rate and magnetic cycle period in stars slowly change together,” said Metcalfe. But when they reach middle-age, he says, their rotation locks and their magnetism eventually decays away.